The invention relates to a particle beam testing method for non-contact testing of interconnect networks for shorts and opens.
As a consequence of the increasing degree of integration and of the progressive miniaturization of semiconductor components, it has become necessary to correspondingly reduce the dimension of the interconnect networks producing the electrical connection between various VLSI circuits. The demand of being able to wire a large plurality of contact points on as small a space as possible therefore led to the development of ceramic multi-layer modules, among other things, in the field of wiring technology. In the meantime, the density of contact points on these modules has become so high that testing their electrical properties with mechanical contact tips can now be carried out only given great difficulty. Electron beam measuring instruments for non-contact testing of interconnect networks for shorts and opens are therefore being increasingly employed. Such an electron beam measuring method is described in IBM Techn. Discl. Bull. Vol. 24, Number 11a, pages 5388-5290, incorporated herein by reference. An installation for the implementation of such a method is disclosed, for example, by European Patent No. 0 066 086 (particularly see FIG. 12 and the appertaining part of the specification), incorporated herein by reference.
The basis for these known methods is the possibility of applying potentials to an insulated specimen with electron beams or documenting existing distributions of potential by detecting the secondary electrons triggered by the primary electron beam. For testing an interconnect network, at least one of the contact points is charged with a first electron beam, and subsequently, the distribution of charge or potential arising in accordance with the network geometry is read with a second electron beam. Electron beams differing in energy are employed for applying and reading the potentials.
The documentation of shorts and opens in a network can occur by comparing the secondary electron signals measured at various contact points. When, for example, the same potential as at the charging point is observed at one of the contact points, i.e. when the same secondary electron current is registered in a secondary electron detector system within the measuring precision given an ideal detector characteristic, then these points are necessarily connected to one another in conductive fashion. When, by contrast, the secondary electron currents differ significantly from one another, then an opens must exist.
In order to prevent a change of the potentials during the reading or sensing with the read beam, the known methods operate with primary energies in the region of the neutral point. Since the primary electron current incident onto the specimen and the secondary electron current emanating from the specimen just compensate under these conditions, the primary electron energy must be modified when changing between a charging and a reading phase. This is technologically achieved in that a plurality of electron beams differing in energy are employed, or in that the high-voltage supply of an electron beam is switched. Both solutions, however, have decided disadvantages. Thus, when switching the high-voltage supply of an electron beam measuring instrument, electron-optical techniques are required in order to retain the position and focusing of the beam on the specimen. In addition, the known electronic difficulties when switching high voltages occur. The employment of a plurality of electron beams also requires a substantial added expenditure for electron-optic components since additional electron sources with corresponding, beam-shaping magnetic coils must be provided.